1. Field of the Invention
The present invention relates to a stator of a torque converter for use in an automotive transmission system. More particularly, the present invention is concerned with a torque converter stator made by molding of a fiber reinforced plastic material and wherein a metallic outer race of a one-way clutch is insert molded.
2. Description of the Prior Art
In an automotive torque converter, a stator having curved vanes is installed between an impeller and a turbine. The stator vanes are made integral with a stator hub which is rotatably supported by a one-way clutch around a turbine shaft for freewheeling in one direction.
The stator hub includes a radial flange for axially positioning an outer race of the one-way clutch. A plurality of axially extending recesses are formed across the radial flange along the inner periphery thereof to form lubricant passages for supplying lubricant to the moving parts of the one-way clutch.
To reduce weight and cost, attempts have been made to build the torque converter stators by injection molding of a fiber reinforced plastic material. However, it has been found that torque converter stators are difficult to manufacture solely with the fiber reinforced plastic material because of high precision required for various dimensional parameters. Accordingly, as disclosed, for example, in Japanese Patent Kokoku Publication No. 63-18050 and Japanese Utility Model Kokai Publication Nos. 3-20754, 4-22210 and 4-27247, there has been proposed in the art to insert mold a metallic outer race of the one-way clutch within the plastic stator hub. However, the problem which must be overcome in injection molding of the torque converter stator incorporating the one-way clutch outer race insert is that cracks are generated in the plastic molding forming the radial flange of the stator hub due to the residual stress resulting from the post-molding shrinkage of the plastic material.
More specifically, during injection molding, the flow of plastic material under pressure coming from an extruder is forced to flow through an axial sprue formed in the molds. The flow is then spread radially outwardly as it flows through a disc gate connecting the sprue with a mold cavity. A plurality of cores which are complementary in shape to the axial lubricant passages are formed in the molds to define the lubricant passages in the molded product. As the plastic material flowing out of the disc gate is infected into the mold cavity, the flow of plastic material is bifurcated around each core and the bifurcated flows thereafter meet and join with each other along a radial plane known in the art as the "weld line".
The presence of the weld line undesirably reduces the tensile strength of the plastic molding as measured in a direction perpendicular to the weld line, because the reinforcing fibers blended in the plastic material tend to be oriented more or less parallel to the weld line. When the plastic molding undergoes the post-molding shrinkage, the residual stress concentrated at the weld line leads to the formation of cracks.
It is therefore the object of the present invention to provide a one-way clutch outer race inserted, plastic torque converter stator which is specifically designed to avoid the formation of cracks along the weld line.